High tibial osteotomy (“HTO”) procedures have become well-established means of treating unicompartmental degenerative arthritis of the knee. This condition occurs due to uneven weight bearing of the femoral condyles on either medial or lateral joint compartments of the tibia. Such uneven weight bearing results from either a varus or valgus defect in the tibia. A varus or valgus defect occurs when the mechanical axis of the knee joint shifts either medially (valgus) or laterally (varus) of the preferred location therefor. It is generally accepted that the preferred location for the mechanical axis of the knee is at 62% of the tibial plateau from medial to lateral. The process for determining the location of the mechanical axis is known in the art. A varus deformity generally results in increased loading on the medial joint compartment, while a valgus defect results in increased loading on the lateral joint compartment. A high-tibial osteotomy procedure uses one of various techniques to bring the knee into proper mechanical alignment by correcting a deformity therein, whether varus or valgus. As used herein when referring to bones or other parts of the body, the term “proximal” means close to the heart and the term “distal” means more distant from the heart. The term “inferior” means toward the feet and the term “superior” means toward the head. The term “anterior” means toward the front part or the face and the term “posterior” means toward the back of the body. The term “medial” means toward the midline of the body and the term “lateral” means away from the midline of the body.
One existing high-tibial osteotomy procedure is what is known as a closing-wedge osteotomy. In such a procedure, a wedge of bone is removed from the tibia and the opening left by the removal is forced closed and secured. The wedge is appropriately shaped to correspond to the appropriate amount of angular correction necessary to bring the knee joint into proper alignment. The procedures for determining both the amount of angular correction and the appropriate wedge shape are known in the art. Generally speaking, however, the wedge is usually shaped so as to span almost the entire medial-lateral width of the tibia, leaving only a narrow “hinge” section of bone on the closed end of the wedge. Once the bone wedge is resected, the opening is forced closed and is typically held in such a position using a staple or other similar device, including bone screws and/or plates. Such procedures are shown in U.S. Pat. No. 5,980,526 to Johnson, et al.; U.S. Pat. No. 6,796,986 to Duffner; U.S. Pat. 5,911,724 to Wehrli; U.S. Pat. No. 5,053,039 to Hoffman, et al.; U.S. Pat. No. 5,540,695 to Levy, and; U.S. Pat. No. 5,601,565 to Huebner.
The closing-wedge HTO procedure has several drawbacks. In particular, the approach (when used to correct a varus deformity) requires a transverse cut to be made from the lateral cortex of the tibia across to near the medial cortex thereof through a moderately sized lateral incision. Since the base length of the wedge spans the entire tibial medial-lateral width, the amount of distance to be closed is quite significant, resulting in shortening of the tibia, which may require corresponding shortening of the fibula. It is problematic to shorten the length of the tibia because this can lead to problems in the gait of the patient leading to back, hip or other joint problems, and can complicate any subsequent total knee replacement (“TKR”) procedure which may be necessary. Further, if shortening of the tibia requires that the fibula be shortened, the HTO procedure is further complicated and patient pain and recovery time are increased. Additionally, tibial shortening leads to a significant amount of soft tissue laxity of the lateral compartment, which includes the joint capsule, lateral collateral ligament, etc. Other complications arise from a closing wedge HTO procedure because the resected tibial plateau is “hinged” medially, for example. This can result in the resected joint being extremely unstable during healing. Subsequent TKR is further complicated by the presence of the staple used to secure the joint during healing because the staple may have to be removed prior to TKR.
An alternative procedure is the opening wedge HTO. In this procedure, a single cut is made from, for example, the medial cortex of the tibia across to near the lateral cortex in order to correct a varus defect (to correct a valgus defect a cut is made from the lateral cortex to near the medial cortex). As with closing wedge HTO, the cut in an opening wedge HTO procedure extends through almost the entire tibia, leaving only enough bone on the lateral tibia to form a hinge section. The cut is then forced open to form a wedge having an angle corresponding to the required amount of angular correction. This procedure can also be used to correct a valgus defect, with the cut originating on the lateral tibia, extending through the tibia to near the lateral tibia. Once the cut is opened, an appropriately shaped wedge can be inserted into the cut to support the tibial plateau at the desired angle. The wedge can be made of a known bone-substitute material, an autograft taken from the patient's iliac crest or an allograft taken from a donor. The wedge is then secured in place using hardware typically in the form of bone plates and screws.
Various disadvantages to the opening wedge HTO exist as well. Specifically, the amount of the distance to be “opened” can be quite significant, leading to lengthening of the leg and an undesirable amount of soft tissue tensioning of, for example, the medial compartment, which includes the joint capsule, the medial collateral ligament, etc. Furthermore, the lateral or medial hinging of the osteotomy makes it extremely unstable, due to the amount of leverage applied to the hinge section from the opposite side of the tibia. This instability makes the knee unable to resist torsional loads applied to the joint. Therefore, it is necessary to secure the cut with bulky plates and/or screws in order to stabilize the joint while it heals. The presence of such hardware can complicate any subsequent TKR procedure which may be required. Additionally, due to the large size of the wedge inserted into the cut, resorption and incorporation of a bone substitute device that may be used to fill the wedge is lengthy. While it is preferred that the wedge be made from autograft material, which is usually removed from the iliac crest of the patient. This harvesting requires a separate procedure to be performed to harvest the autograft, which adds time, pain, blood loss and the risk of infection to the procedure. Therefore various allograft implants have been designed to fill the wedge as illustrated in U.S. Pat. No. 6,575,982 to Bonutti, and in U.S. Pat. Pub. No. 2005/0075641 to Singhatat, et al. These implants generally are made of a biologically compactable material and may include features to promote affixation to the bone and/or bony ingrowth. Alternatively, the wedge can be left unfilled, the tibial plateau being supported by plate or bracket such as those shown in U.S. Pat. No. 6,823,871 to Schmieding and U.S. Pat. Pub. No. 2003/0195516 to Sterett.
Various tools have been developed in order to facilitate both the opening and closing wedge osteotomy procedure. Typically, these include cutting guide surfaces which are capable of being affixed to the bone and provide a surface which is used to guide a bone saw or other known instrument into proper alignment for the desired cut or cuts. Typically, these guides are designed to affix to either the medial or lateral side of the tibia, depending on the type of correction required and the procedure used. By taking either a medial or lateral approach for cutting, the patellar tendon is easily avoided; however, these approaches make alignment of cuts more difficult, because the mechanical axis is not visible from the side of the knee.
A further alternative procedure known in the art is a dome tibial osteotomy. In this procedure, the entire proximal tibia, as well as the proximal fibula are detached from the remaining tibia using a curved or dome-shaped bone cut. The proximal tibia is then repositioned in the correct alignment and secured in place with various forms of hardware, which can include staples, plates, screws, or cerclage wire. The total bisection of both the proximal tibia and fibula leads to an extremely unstable joint, which requires a great deal of hardware for stabilization, which would, most likely, need to be removed prior to subsequent TKR. This procedure is advantageous because it neither shortens nor lengthens the leg to a problematic extent. However, it is generally regarded as too invasive or risky for practical purposes.